PROJECT SUMMARY: The purpose of the proposed project is to combine wideband acoustic immittance (WAI) and middle-ear muscle reflex (MEMR) testing using new approaches that improve sensitivity, increase test efficiency, and provide objectivity in interpretation. Acoustically elicited MEMRs have a long history of value in the clinical evaluation of hearing loss. While sensitive to and affected by middle-ear disorders linked to conductive hearing losses, MEMRs demonstrate particular sensitivity to synaptic and post-synaptic disorders related to the VIIIth nerve and auditory brainstem pathways through activation of neural pathways ipsilateral and contralateral to the physiologic middle-ear response. MEMRs are objective in providing information in a brief period of time without requiring behavioral responses from the patient and this objectivity facilitates their use in infants. Measuring MEMRs in the context of WAI provides clear advantages over current methods based on the ability to evaluate responses over a broader frequency range and to elicit responses to lower-intensity stimuli. The broadband nature of WAI is a well-documented advantage in infant testing. Despite the fact that MEMR is a robust and sensitive measure, it is under utilized clinically, based on factors that include subjectivity in response determination, intrasubject variation, uncertainty about MEMR response presence, and lack of confidence among clinicians in interpreting responses. We propose development of an instrument that will provide a new and sensitive approach to objective measurement of MEMR using a WAI approach. Creating the hardware and software using this approach should reduce subjectivity in clinician interpretation and encourage increased clinical utilization and application in patients of all ages. The specific aims of this project are to build a prototype instrument that is capable of measuring WAI-based MEMR for both ipsilateral and contralateral reflex pathways. A pilot study presented in this application shows clear differences between subjects with normal auditory function and responses obtained from a passive coupler and a patient known to lack MEMRs. The ipsilateral hardware and software that allowed the pilot study will be integrated into the new commercial system. The binaural system necessary for contralateral reflex measurement will be developed as a dual- channel Mimosa Acoustics system. Phase I human subject data collection will be completed on a small number of infants, adults with normal hearing, and adults with known hearing losses to demonstrate efficacy of the new system and method. The results obtained in the Phase I project will inform development of software tools for analysis and display and will guide plans for the Phase II application. This will involve further development of the dual-channel system to achieve additional new approaches to MEMR measurement, refinement of recording and analysis methods, and testing in larger clinical populations in the context of auditory screening and diagnostic applications.